1. Field of the Invention
The present invention relates to a process for forming a hydrophilic coating and a hydrophilic coating formed by such process, and a process for forming an ink jet recording head including the hydrophilic coating and an ink jet recording head formed by such process.
2. Description of the Related Art
A technology for performing patterning by processing a resin composition by photolithography is applied in a variety of fields. Examples of the technology include a process for forming an ink jet recording head.
An ink jet recording head for performing recording by ejecting ink onto a recording medium generally includes multiple fine ink ejection orifices, ink flow paths, and energy generating elements for generating energy necessary for ejecting ink to be provided in parts of the ink flow paths.
Japanese Examined Patent Publication No. H06-45242 describes a process of producing such ink jet recording head. First, an ink flow path pattern is formed with a soluble resin on a substrate having energy generating elements formed thereon. Next, a coating resin layer including a cationic polymerization resin and a photoacid generator is formed on the ink flow path pattern, and ink ejection orifices are formed above the energy generating elements by photolithography. Finally, the soluble resin is dissolved and the coating resin layer is then cured to form an ink flow path member.
In general, in order to achieve high printing quality and constantly provide a stable printing effect in an ink jet printer, it is necessary that ink to be ejected from ink ejection orifices be constantly ejected in a vertical direction with respect to an ink ejection orifice surface. When a non-uniform ink pool is present in the ink ejection orifice surface at the time of ejection or the pool is formed during the ejection, ink to be ejected is attracted into the ink pool, and the flying direction of each of ink droplets deviates from the normal direction, with the result that normal ejection is not achieved in some cases. Further, when the array density of ink ejection orifices is increased in order to improve printing quality, an array distance between the ink ejection orifices becomes shorter depending on the increase, and hence the ejection is more liable to be affected by the non-uniform ink pool in the ink ejection orifice surface.
In view of the foregoing, there have been reported a large number of proposals concerning solving the above-mentioned problems by subjecting an ink ejection orifice surface to water-repellent treatment for repelling ink, thereby providing stable ink droplets. Further, in contrast, there has also been reported a proposal concerning ensuring uniform wetness in an ink ejection orifice surface by subjecting the ink ejection orifice surface to hydrophilic treatment for wetting the surface with ink.
Japanese Patent Application Laid-Open No. H06-122210 describes those surface treatment processes. For example, examples of the process for subjecting an ink ejection orifice surface to water-repellent treatment include a process including applying a fluorine-based water repellent. Meanwhile, examples of the process for subjecting an ink ejection orifice surface to hydrophilic treatment include a process including performing hydrophilization by generating a polar group in the ink ejection orifice surface by acid treatment, plasma treatment, or the like.
As described above, the conventional processes each require an apparatus exclusively used for acid treatment, plasma treatment, or the like in the formation of a hydrophilic coating, and the hydrophilic coating cannot be formed with a photolithography apparatus alone, with the result that a large burden is imposed in some cases.
As described above, even in the case where an ink jet recording head is formed by photolithography, a process including applying a fluorine-based water repellent or the like has only to be employed in order to subject an ink ejection orifice surface to water-repellent treatment, and a conventional apparatus may be used. However, an apparatus exclusively used for acid treatment, plasma treatment, or the like is required for subjecting the ink ejection orifice surface to the hydrophilic treatment, and the hydrophilic coating cannot be formed with the conventional apparatus alone, with the result that a large burden is imposed on a forming step in some cases.
An object of the present invention is to provide a process for forming a hydrophilic coating easily by photolithography without requiring any apparatus exclusively used for hydrophilic treatment and a hydrophilic coating formed by the process. Another object of the present invention is to provide a process for forming an ink jet recording head including the hydrophilic coating and an ink jet recording head formed by the process.